Electrical-resistance pyrometry.



No. 834,162. PATENTED OCT. 23, 1906. E. F. NORTHRUP.

ELECTRICAL RESISTANCE PYROMETRY.

APPLICATION FILED JUNE 16.1906.

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Fig.1.

aww/wboz PATENTED OCT. 23, 1906.

B. P. NORTHRUP.

ELECTRICAL RESISTANCE PYROMETRY.

APPLICATION FILED JUNE 16,1906.

2 SHEETSSHEET'2.

Electrical-Resistance Pyrometry, of

UNITED sr rns PATENT orrion.

EDWIN F. NORTHRUP, OF PHILADELFHIA, PENNSYLVANIA, ASSIGNOR TO THE LEEDS & NORTHRUP COMPANY, OF PHILADELPHIA, PENNSYL- VANIA, A CORPORATION OF PENNSYLVANIA.

ELECTRICAL-RESISTANCE PY ROM ETRY.

To all whom it may concern:

Be it known that I, EDWIN F. Non'rmwr, a citizen of the UnitedStates, residing at Philadelphia, in the county of Philadelphia and State of Pennsylvania, have invented certain new and useful Improvements in which the following is a specification.

There are two general methods of measur-' ing temperatures electrically. One is known as thermo-electric pyrometry and the other as electrical-resistance pyrometry.

In thermo-electric pyrometry temperature is measured by means of the thermo-electric couple by measuring the electromotive forces that are setup when the junctions of the dissimilar metals comprising the couple are exposed to different temperatures.

In electrical-resistance yrometry temper ature is measured by the c ianges in electrical resistance of a conductor, usually a platinum wire, and depends upon the property of such conductor to change in resistance with the tem erature.

T ere are also in use two methods of electrical resistance pyrometry, one known as the Wheatstone-bridge method and the other as the potentiometer method. In the former the temperature is measured by balancing the resistance of the slide-wire of a W'heatstone bridge, the scale of which is calibrated in degrees of temperature with the resistance of a high-resistance coil of an electrical-resistance thermometer.

In the potentiometer method the temperature is measured by comparing the otential drop over the high-resistance .coil 0 an electrical-resistance thermometer with the drop in potential through a standard known resistance by means of a potentiometer. In the thermometer usedin this method the measuring-current is led to and away from the resistance-coil by two current-leads, and two other leads known as potential-leads, pass down the stem of the thermometer and are taplped onto the terminals of the resistancecoi The method employed in carryin out the present invention is both a potentia method and a brid e method, though employing neither the eatstone bridge nor .the potentiometer. It differs also from the forego- Specification of Letters Patent.

Application filed June 18,1906.

Patented Oct. 23, 1908. Serial No. 322,063

ing methods in that in the thermometer employed the high-resistance coil mentioned in connection with the foregoing methods may be su )planted by a coil of low resistance, thoug the two current-leads and potentialleads, are still em loyed. This method may therefore be cal ed a potential-bridge method, in which the temperature is measured by comparing the potential drop of a low-resistance coil of an electrical-resistance thermometer with the potential drop through the resistance of the slide-wire of a Kelvin low-resistance bridge.

The resistance-thermometer as designed for hi h-temperature work if wound to a suitable resistance for use in either the Wheatstone-bridge or potentiometer method is necessarily of considerable size. This uniits such thermometers as compared with thermocou )les for taking the temperatures of small places or points. Moreover, these thermometers besides requiring considerable skill to construct are costly and more or less fragile, the resistance usually consisting of a coil of fineplatinum wire wound upon a delicate mica support, while the leads to the coil are supported-by delicate mica washers.

The disadvantages above pointed out, as Well as others encountered in electrical-resistan'ce pyrometry, are sought to be overcome by the present invention.

In order to fully describe my said invention, reference will be had to the accompanying drawings, forming a part of this application, and in which Figure 1 is a dia ram of the connections of a Kelvin bridge or measuring low resistances Fig. 2, a diagram of electrical connections employed in carrying out the present invention; Fig. 3, a longitudinal central sectional view of an electrical-resistance thermometer embodying my present in ention; Fig. 4, an end elevation of the same; and Fig. 5, a section taken on the line 5 5, Fig. 3.

The bridge connections devised by Lord Kelvin for the measurement of low resistances is well known in the art; but since they constitute such an important part of the present invention a brief description thereof will be given, reference being had to Fig. 1. A Kelvin bridge consists, essentially, of a low-resistance conductor embraced between the points B, which is usually a standard of comparison; a low-resistance conductor embraced between the points 0 D, which is usually the conductor whose resistance is to be measured or compared with the resistance of the conductor between A B; a low-resistance yoke B D; resistances a a. of known value, connected by contacts land 2, one or both of which may be movable, to conductorAB; resistances b b of known value, connected by contacts 3 and '4, respectively, one or both of which may be movable, to conductor 0 D; a galvanometer G, connected between resistances a and b on one side and between resistances a and b on the other side, and terminals A and O for connection to a source of electric current. Calling the resistance between 1 and 2 R and between 3 and 4 X, the bridge is balanced when ag; b 6 R the first two terms being made equal by construction,

Therefore, since a b and R are all known values the unknown value X may be readily determined.

In using the Kelvin bridge for the measurement of temperatures according to my invention it is not necessary to determine any actual values of resistance. It is only necessary that the resistance of the resistance-wire of the thermometer for a given temperature shall balance that of a given length of conductor included between two points on the bridge or slide wire, so that the length of said latter conductor may be laid off in degrees of temperature corres onding to different points thereon of the s iding bridge-contacts, which will effect a balance with the resistance of the thermometer resistance-wire at those temperatures. By the Kelvin-bridge connections .01 ohm may be measured with as great precision as one hundred ohms may be measured by the ordinary bridge methods. By taking advantage of the Kelvin bridge as a reading device I have found that high temperatures may be measured by the use of a very low-resistance thermometer, which is a great advantage, as above pointed out.

Connections whereby temperatures may be measured by one or severe thermometers according to my invention are shown in Fig. 2, where T, T T and T represent four potential-point thermometers of low resistance, each having a small-resistance conductor 5, preferably of N o. 20 Haraeus platinum wire having a resistance of about .05 ohms at 20 centi ade 6 and 7, current-leads passing from bin ing-posts 8 and 9 to the terminals of said resistance 5, and 10 and 11 potentialleads passing from binding-posts 12 and 13 15, where they are fused to the resistance-wire 5.

. A 0 represent the bridge-terminals for connection to the source of measuring-cup rent; C D, the bridge or slide wire; 1* 7'', two resistance-coils for extending the ra e of said bridge-wire; E a plu switch for sald resistance-coils; 1000 .(2 am? 100 .(2,"the four ratio-coils corres onding to resistances a a and b b, Fig. 1; the bridgealvanometer; F, a scale for the bridge-wire, aid off in degrees of temperature, and 4 or said wire.

To measure temperature by one of the thermometers-T, for examplethe binding-post 9 is connected to the post D to form the yoke of the bridge corresponding to the conductor B D, Fig. 1, the binding-post 8 is connected to the ositive binding-post A, and the potentialead binding-posts 12 ard 13 are connected to the two resistances indicated 1000 .Q. The plug 6 is inserted in one of the sockets of its switch, and the contact 4 is slid along the bridge-wire until the galvanometer shows no deflection. When this occurs, the potential drop over 3 4 will equal the potential drop over 14 15that is, over resistance-wire of thermometer-which shows that the resistance between 3 and 4 equals resistance of wire 5 between 14 and 15. Therefore if the bridge-wire is rovided with a scale F laid off in degrees 0 temperature and calibrated so that each de eemark will correspond to a posit-ion o the sliding contact 4, which will effect a balance of the bridge when the resistance-coil of the thermometer is subjected to that degree of temperature,.it will be readily seen that the bridge may be made to read directly in degrees of temperature.

The arrangement of connections shown is of course not confined to the specific values of the ratio-coils given, as these may range as high as five thousand ohms or more or may be lower than that heretofore stated.

By connecting the potential-leads of each thermometer and the right-hand currentconductor of the several thermometers, respectively, to three contacts of the switches S, 8*, S, and S and providin the bridges with movable contacts S, whic may be shifted from one set of contacts to the next, temperatures may be measured with the several thermometers, at the same time keeping the resistance of the yoke of the bridge low, as required by theory.

low-resistance thermometer constructed according to my invention is shown in Figs. 3 to 5, inclusive, where parts corres onding to those mentioned in connection wit Fig. 2 are indicated by similar reference-numerals. This thermometer consists, among other parts, of a tube 16, preferably of porcelain or other suitable substance, hermetically closed at one end, as at 17, and closed at its other to potential points 14 and a sliding contact BEST "VAILALBLE CQPY end by a plug or mica washer 18. Within this tube are located four non-conducting tubes 19, preferably of porcelain, through which pass the current-ca wires 6 7 and the potential-leads 10 11, the said tubes being supported by washers 18, 20, 21, and 22, of mica or other suitable material. The resistance-wire 5 is preferably coiled into two spirals 5 and 5 and is supported at one end in a Washer 23, refera y of mica. The other end of the tu e 16 extends into and fits tightly an opening 24, passing longitudinally through the center of a cylindrical head 25, preferably of boxwood, to which are secured the'four terminal binding-posts 8, 9, 12, and

13, to which are connected the current-carry ing and potential leads, as shown. Each of sald binding-posts is held against rotation in said head by a key 26. The end of the central opening of the head 25 nearest the bindingposts is closed by a screw-plu 27. By removing this plug the termina connections between the lead-wires and the binding-posts may be readily gotten at.

Surrounding the tube 16 for a short distance from the head of the thermometer is a metal tube 28, which is brazed at one end into a metal cap 29, fixed to one end oiv the head 25.

The current and potential leads are preferably of a cheaper grade of platinum than the resistance-wire 5. This is an advantage, on account of the fact that impure latinum has a lower temperature-coefiicient t an that of ure platinum.

thermometer constructed as above described is a great deal simpler and easier to make than the fragile and delicate resistancethermometers at present in use for measuring high temperatures, and, owing to the fact that they may be made smaller than those hitherto employed, thermometers constructed according to my invention may be used in places where it is impracticable to use the others. Moreover, in the method herein employed the measuring-current does not have to be held constant during the'measurement, as in the case of the potentiometer method-that is, it is independent of the variations in said current.

What I claim is 1. A low-resistance thermometer, having potential-leads and current-leads, and a Kelvin bridge in which said leads are connected, to measure temperatures.

2. A low-resistance thermometer, having potential-leads and current-leads, and a Kelvin bridge in which said leads are connected to measure temperatures, said bridge being arranged to read directly in degrees of temperatures.

3. A lurality of low-resistance thermometers eac havin potential-leads and currentleads, a Kelvi'niridge, and means to connect one or more of said thermometers in said bridge to measure temperatures.

4. An electrical-resistance thermometer comprising a tube, a low-resistance tempera' ture-measuring conductor mounted in said tube near one end thereof, current-leads passing down said tube to said conductor, and potential-leads passing down said tube to potential points on said conductor.

5. An electrical-resistance thermometer, comprising a porcelain tube, a low-resistance temperature-measuring conductor within said tube near one end thereof, supports for said conductor, insulating-tubes within said porcelain tube and extending approximately the length thereof, current-leads and potential-leads each passing down a separate one of said insulating-tubes and connected to the said resistance-conductor, a head into which one end of said porcelain tube extends, binding-posts on said head connected with said current and potential leads, an exterior metal tube fitting over the porcelain tube near said head, and a metal cap into which said metal tube extends, secured to the face of said head.

In testimony whereof I aflix my signature in presence of two witnesses.

EDWIN F. NORTHRUP. 

